Abstract We studied the energy¯ow from C 3 and C 4 plants to higher trophic levels in a central Amazonian savanna by comparing the carbon stable-isotope ratios of potential food plants to the isotope ratios of species of dierent consumer groups. All C 4 plants encountered in our study area were grasses and all C 3 plants were bushes, shrubs or vines. Dierences in d 13 C ratios among bushes (" x = A30.8, SD = 1.2), vines (" x = A30.7, SD = 0.46) and trees (" x = A29.7, SD = 1.5) were small. However the mean d 13 C ratio of dicotyledonous plants (" x = A30.4, SD = 1.3) was much more negative than that of the most common grasses (" x = A13.4, SD = 0.27). The insect primary consumers had d 13 C ratios which ranged from a mean of A29.5 (SD = 0.47) for the grasshopper Tropidacris collaris to a mean of A14.7 (SD = 0.56) for a termite (Nasutitermes sp.), a range similar to that of the vegetation
